The deep biosphere, found beneath the Earth's surface, is a unique habitat for microbes that has been studied to understand ancient life and the boundaries of life on Earth. Recent research has shown that microbial processes and species in the subsurface crust are different from those in surface soils and oceans. By studying minerals and isotopes, scientists have been able to directly date microbial activity and gain insights into the evolution of the deep biosphere over time. This research sheds light on how life has adapted to survive in extreme environments and provides clues about ancient life on Earth, with potential implications for astrobiology.